Angular momentum of vacuum bubbles in a first-order phase transition

TL;DR

This paper estimates the spin of primordial black holes formed during a first-order phase transition in a dark sector, revealing a wide range of possible spins influenced by phase transition parameters.

Contribution

It presents the first calculation of the spin of false vacuum bubbles induced by cosmological perturbations during a FOPT in a dark sector.

Findings

The spin parameter varies from 10^{-5} to 10 for different FOPT energies.

A scaling relation links the root-mean-square spin to FOPT time scale, bubble wall velocity, and temperature ratio.

The spin distribution depends on the dark sector's temperature relative to the visible sector.

Abstract

The formation of primordial black holes (PBHs) during a first-order phase transition (FOPT) in a dark sector has been of recent interest. A quantity that characterizes a black hole is its spin. We carry out the first step towards determining the spin of such PBHs, by calculating the spin of spherical false vacuum bubbles induced by cosmological perturbations. The angular momentum is given by the product of density and velocity perturbations. We carefully track the evolution of background quantities and calculate the transfer functions during the FOPT. We find that the dimensionless spin parameter $s = J/(G_{\rm N} M^2)$ of false vacuum bubbles of mass $M$ and angular momentum $J$, take a wide range of values from ${\cal{O}}(10^{-5})$ to ${\cal{O}}(10)$ for FOPTs between 10 keV and 100 GeV and a dark sector that is 0.1 to 0.4 times cooler than the visible sector. We also find a scaling relation between the root-mean-square value of the spin, the FOPT time scale, the bubble wall velocity, and the dark sector-to-visible sector temperature ratio.